Inverter devices adjust voltage and frequency, thereby controlling the ascent and descent speed of elevators, cranes, multistory parking garages, printing machines, and others.
Patent Literature 1 discloses an inverter device that prevents an induction motor for winding and rewinding a winch cable from going into an excessive torque state. The inverter device in Patent Literature 1 has an inverter main circuit controlled by PI control. When torque current detected by a torque current detection circuit exceeds a set level, causing the excessive torque state, the frequency and voltage of AC voltage generated by an inverter are determined, based on the speed of the induction motor output from a speed detector.